Optical device for use with a slit lamp biomicroscope

ABSTRACT

An optical device comprising a lens and an adjustable lens holder which is adapted to be positioned on an existing slit lamp biomicroscope such that the lens may be selectively positioned in the path of the illuminating light beam from the slit lamp light source. In one embodiment of the invention, the adjustable holder is designed to be rotatably positioned in association with the slit lamp light illumination apparatus and in relation to the projecting or objective lens of the slit lamp illumination system. The lens holder is designed to pass a narrowed zone on support structures associated with the light illumination apparatus and to frictionally engage a portion of the support structure while allowing rotation of the lens into and out of the path of the illuminating light beam. Alternatively, as the design of the slit lamp biomicroscope varies, the lens holder may vary so as to allow frictional engagement with a portion of the illuminating light source structure, wherein the lens will be pivotable into and out of the path of the illuminating light beam adjacent the projecting lens of the slit lamp light source. The lens of the optical device can be made of glass or plastic, and the lens holder may be constructed so as to allow various lenses to be quickly and easily removed and replaced by another lens. Alternatively, the lens holder may be provided with a plurality of lenses which may be selectively positioned in the path of the illuminating light beam. Additionally, a plurality of the optical devices may be used with the same slit lamp biomicroscope to modify the optical characteristics of the light source selectively and efficiently. Modification may include filtering of the illuminating light or adding divergence of convergence to the light rays to achieve various desired optical characteristics.

This is a continuation of application Ser. No. 07/604,547, filed on Oct.29, 1990, now a U.S. Pat. No. 5,216,456.

BACKGROUND OF THE INVENTION

The present invention is directed an optical device which is utilized inconjunction with a slit lamp biomicroscope, when the biomicroscope isused for indirect ophthalmoscopy or other examination procedures, so asto obtain desired optical characteristics by modifying the illuminatinglight beam emitted from the projecting lens of the slit lampbiomicroscope. More particularly, the invention is directed to anoptical device which may be simply positioned and retained on aconventional state-of-the-art slit lamp biomicroscope in associationwith the projecting lens thereof to modify the illuminating light beamby filtering, enlarging or otherwise modifying the beam.

The slit lamp biomicroscope has long been utilized as a tool forophthalmic examinations such as indirect ophthalmoscopy, gonioscopy,fundoscopy or the like. Various forms of slit lamp biomicroscopes havebeen developed such as the Haag-Streit slit lamps or the Zeiss slitlamps, which essentially achieve similar desired characteristics in thebiomicroscope, but have been designed somewhat differently.Conventionally, the slit lamp biomicroscope includes a microscope head,an illumination system producing a slit beam which may be rotated ortilted by the user, as well as patient support structure to facilitate aproper and comfortable examination. In particular, the illuminationsystem of the slit lamp biomicroscope varies with manufacturing designs,but in most cases will allow the slit light beam to be rotated 90° fromvertical and may also allow the light path to be inclinable by an angleranging between 0° and 20°. The entire illumination assembly may betilted to provide these characteristics or tilting may be accomplishedby a rotatory prism or tilting mirror structure. The beam size is alsoadjustable from an extremely narrow slit to several millimeters inwidth, and the height of the slit may be controlled by a variable sizeaperture or diaphragm structure.

Using a slit lamp biomicroscope, observation of particular aspects ofthe examined eye may be enhanced by only transmitting particularportions of the light spectrum found in the illuminating light beam fromthe slit lamp light source. Various state-of-the-art slit lampbiomicroscopes have recently included built-in color filters to allowenhanced observation of different aspects of the examined eye. Forexample, a red filter may be utilized so as to better enable observationof blood vessels on the fundus of the eye. Although various filters havebeen built in slit lamp biomicroscopes, other desirable characteristicshave not been built in to the biomicroscopes and therefore are notavailable for use during various examination techniques. Similarly, manyslit lamp biomicroscopes are not provided with any filtering apparatusat all, or may only include several of the possible desired filters.

Under many circumstances, an indirect ophthalmoscopy lens device is usedfor examination of a patient, wherein the illuminating light beam fromthe slit lamp biomicroscope light source is directed through theindirect ophthalmoscopy lens which is held adjacent to the patient'seye. In use with an indirect ophthalmoscopy lens, the maximum possiblesize of the illuminating light beam reaching the indirect ophthalmoscopylens is no more than 12 mm in diameter for state-of-the-artbiomicroscopes. The indirect ophthalmoscopy lens itself may be ofrelatively large diameter, and it would be desirable to enableeliminating light beam from the slit lamp light source to fullyilluminate the indirect ophthalmoscopy lens for full illumination of theexamined eye.

SUMMARY OF THE INVENTION

Based upon the foregoing, there is found to be a need for an opticaldevice which may be simply added or retrofit to the slit lampbiomicroscope to modify the size, color, polarization or other aspectsof the illuminating light beam from the slit lamp light source and usedfor illumination in various examination techniques. It is therefore amain object of the invention to provide an optical device which is addedor retrofit to the state-of-the-art slit lamp biomicroscope to enableselective modification of the illuminating light beam from thebiomicroscope.

Another object of the invention is to provide an optical device for usewith an existing slit lamp biomicroscope which will allow modificationof the illuminating light beam from the slit lamp light source in aselective and variable manner, and may include filtering means,polarizing means or other means by which the optical characteristics ofthe illuminating light beam are modified.

It is another object of the invention to provide an optical device foruse with an existing slit lamp biomicroscope to enable repositioning ofthe image of the filament of the slit lamp light source so as tofacilitate examination procedures such as indirect ophthalmoscopy.

It is another object of the invention to provide an optical device whichwill enable the size of the illuminating light beam from the slit lamplight source to be increased in size to facilitate various examinationprocedures.

These and other objects of the invention are achieved by an opticaldevice comprising a lens and an adjustable lens holder which is adaptedto be positioned on an existing slit lamp biomicroscope such that thelens may be selectively positioned in the path of the illuminating lightbeam from the slit lamp light source. In one embodiment of theinvention, the adjustable holder is designed to be rotatably positionedin association with the slit lamp light illumination apparatus and inrelation to the projecting or objective lens of the slit lampillumination system. The lens holder is designed to pass a narrowed zoneon support structures associated with the light illumination apparatusand to frictionally engage a portion of the support structure whileallowing rotation of the lens into and out of the path of theilluminating light beam. Alternatively, as the design of the slit lampbiomicroscope varies, the lens holder may vary so as to allow frictionalengagement with a portion of the illuminating light source structure,wherein the lens will be pivotable into and out of the path of theilluminating light beam adjacent the projecting lens of the slit lamplight source. The lens of the optical device can be made of glass orplastic, and the lens holder may be constructed so as to allow variouslenses to be quickly and easily removed and replaced by another lens.Alternatively, the lens holder may be provided with a plurality oflenses which may be selectively positioned in the path of theilluminating light beam. Additionally, a plurality of the opticaldevices may be used with the same slit lamp biomicroscope to modify theoptical characteristics of the light source selectively and efficiently.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the optical device will becomeapparent upon a further reading of the detailed description inconjunction with the drawings wherein:

FIG. 1 shows a conventional state-of-the-art slit lamp biomicroscopewith the optical device of the invention operatively positioned thereon;

FIG. 2 as an enlarged cut away view of the slit lamp biomicroscope asseen in FIG. 1, showing positioning of the optical device thereon;

FIG. 3 is an enlarged perspective view of a first embodiment of theoptical device for use with the slit lamp biomicroscope as seen in FIG.1;

FIG. 4 is an enlarged top view of the optical device as seen in FIG. 3;

FIG. 5 is an enlarged side elevation of the optical device as seen inFIG. 3;

FIG. 6 is an enlarged top elevational view of an alternate embodiment ofthe optical device of the invention;

FIG. 7 shows another type of slit lamp biomicroscope with an alternateembodiment of the optical device positioned thereon;

FIG. 8 is an enlarged top elevational view of the optical device for usewith a slit lamp biomicroscope as seen in FIG. 7;

FIG. 9 is an alternate embodiment of the optical device for use with aslit lamp biomicroscope as seen in FIG. 7; and

FIG. 10 is a schematic illustration of the illuminating system of a slitlamp biomicroscope including placement of the optical device of theinvention in the path of the illuminating light beam from the slit lamplight source, wherein the lens of the device has dioptric power whichincreases the divergence of the light beam from the slit lamp lightsource incident upon an indirect ophthalmoscopy lens.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, there is shown a conventional state-of-the-artslit lamp biomicroscope 10, manufactured by Haag-Streit, which isavailable in the market. The biomicroscope 10 is designed forobservation of the eye, and includes various structure to facilitatesuch observation. The microscope head 12 includes eye pieces which canbe corrected to the accommodating error of the physician and is usableto magnify a produced image by 5 to 45 times, as an example. A patientsupport structure 14 includes a chin and forehead rest for the comfortof the patient as well as to maintain position of the examined eyeduring examination. The illumination system 16 generally includes anilluminating light source 18, and a lens system with one or more lenses(not shown) disposed in the path of the light beam originating from asmall filament within the biomicroscope. The lens system acts to refractthe light beam to create a diverging bundle of light rays. The divergingbundle of light rays is directed through a projecting or objective lens20, forming an exit opening of the illumination systems to a reflectingmirror 22 so as to be directed toward the eye or an indirectophthalmoscopy lens utilized for examination of a patient. Theillumination system 16 includes a slit beam adjustment 24 as well asadjustment for centering or decentering the slit image at 26. In suchadjustments, the position of the projecting lens 20 is not modified, butthe position of the reflecting mirror 22 may be. The entire illuminationsystem as well as microscope system may be raised or lowered for properexamination of a particular patient. The optical device of the inventionis shown at 28 and provides a lens within a lens holder which ispositioned between the projecting lens 20 and reflecting mirror 22 ofthe slit lamp biomicroscope 10. In the biomicroscope 10 as shown in FIG.1, the lens holder may be positioned on supporting structure of theillumination system so as to be selectively positioned in the path ofthe illuminating light beam regardless of the adjustments made withrespect to the slit image.

Turning now to FIG. 2, the positioning and operation of a firstembodiment of the optical device of the invention will become moreapparent. The area of the projecting lens 20 of the illumination system16 of the biomicroscope is shown enlarged with the optical device 28thereon. The optical device 28 includes a lens holder 30 with a firstbody portion 32 which is adapted to engage a supporting bar 34associated with the illumination system 16. The supporting bar 34includes a narrowed portion 36 which allows for binocular vision usingthe microscope portion of the biomicroscope without interference fromthese supporting bars. The first body portion 32 of the device 28therefore includes a semi-circular body with a longitudinal gap allowingthe body portion 32 to be slipped over the narrowed portion 36 of thesupporting bar 34. The lens holder 30 may be constructed of a resilientmaterial such as plastic such that the longitudinal gap in the bodyportion 32 may be spread apart slightly to fit around narrowed portion36 of the supporting bar 34. .The inside diameter of the semi-circularbody portion 32 then corresponds to the diameter of the supporting bar34 so as to frictionally engage the bar 34 at locations of normaldiameter adjacent to narrowed portion 36. It should be evident that inthis manner, the optical device 28 may be slipped on to the supportingbar 34 to an operative position relative to the projecting lens 20 andreflecting mirror 22 by properly positioning the lens portion 38 at thegap between projecting lens 20 and reflecting mirror 22 and rotatinglens holder 30 to the position as seen in FIG. 2. Thus, selective use ofthe optical device 28 is accomplished very easily and effectively whenmodification of the optical characteristics of the illuminating lightbeam are desired.

The optical device of this embodiment is seen in more detail in FIGS.3-5, wherein the lens holder 30 includes the first body portion 32 beingof semi-circular configuration and having a gap 40 formed therein havingdimensions to allow the body portion 32 to slip over the supportstructure of the illuminating system of a biomicroscope as previouslydescribed. The inner diameter of the semi-circular portion of bodymember 32 as shown by A in FIG. 4 is of slightly smaller diameter thanthe supporting structure of the illumination system such that thesemi-circular portion will frictional engagement with the supportstructure and yet allow longitudinal and rotational movement of the bodyportion thereon. The body portion 32 may also include outwardlyextending projections 42 to more easily allow the user to rotate bodymember 32 on the support structure of the biomicroscope.

The optical device 28 may further comprise a lens holding portion 44extending from the semi-circular portion 32 in adapted to engage andsecure a lens 38 therein. The lens holding portion 44 may be adapted toengage and secure the lens 38 by means of suitable structure such astabs 46 and 48 creating a suitable slot in the lens holding portion 44for positioning lens 38. It also may desirable to provide a means bywhich the lens 38 can be removed and replaced with another type of lensto allow the optical device 28 to be adapted for a variety of uses. Asuitable means may be a pivotable flange 50 extending from one edge ofthe opening in lens holding portion 44, which may be pivoted into a lensengaging position for retention of lens 38 in the portion 44, or pivotedto a non-lens engaging position for removal of lens 38. Other suitablemeans may be provided for allowing the lens 38 to be removed andreplaced selectively by the user.

The dimensions of the lens holding portion 44 are such that the lens 38extends entirely over the projecting lens 20 of the slit lampbiomicroscope as seen in FIGS. 1 and 2 and allows for adjustment of theslit beam without degrading the modification of optical characteristicsaccomplished by lens 38. The optical device 28 as seen in these figuresis shown as having a rectangular lens portion 38, but any desired shapemay be utilized as for example a generally circular shape or havingconvex or concave surfaces thereon.

In the invention, modification of the illuminating beam generated by thebiomicroscope may include filtering of the illuminating light by any ofa variety of filters such as colored filters or polarizing filters. Inthe case of color filters, the lens 38 may be constructed of ahomogeneous transparent plastic material or a homogeneous transparentglass material in which the spectral transmission characteristics of thetransparent optical material is high. The filtering lenses may comprisean orange-red colored optical material which will limit the spectraltransmission of the illuminating light to the yellow-orange-red portionof the visible spectrum, so as to cut out green portions of theilluminating light to better enable observation of blood vessels in theeye. Alternatively, a green colored optical material may limit thespectral transmission to the green portion of the visible spectrum toeliminate red portions thereof and to enable observation of the nervefiber layer in the eye. A yellow colored optical material will enablespectral transmission of the green-yellow-orange-red portion of thevisible spectrum which will eliminate blue and violet portions thereofto provide patient safety and comfort. The optical material may comprisea dichroic filter glass or the like. As still another example, theoptical material may be transparent to the visible spectrum, but may actto filter portions of the non-visible spectrum which may be present inthe illuminating light.

In another desirable embodiment, the lens 38 may be a polarizing lens,wherein the light from the slit lamp light source is refracted throughthe lens to be polarized in a specific direction. If a polarizingfilter, with its direction of polarization at 90° to the direction ofpolarization of the incident light beam, is placed in front of bothobjective lenses of the biomicroscope, the unwanted specular or glarereflection from an indirect ophthalmoscopy lens and cornea, whichremains polarized in the same direction as the incident light beam, willnot be transmitted through the polaroid filter. In this way, the aerialimage of the fundus as produced by the indirect ophthalmoscopy lens willbe seen clearly and without overlying annoying glare spots. The use of apolarizing filter to remove glare is especially useful whenphotographing the aerial image of the fundus utilizing the slit lampbiomicroscope in conjunction with an attached camera. The lens 38 may bea single element of glass or plastic or may be a composite lensconsisting of a clear white portion combined with a colored filter orpolarizing filter or both.

In another desired embodiment, the lens used in association with theoptical device may be a lens having refractive power, such as a negativepower or positive power lens. Such a lens may be desirable in that ithas been found that with the maximum slit opening of the biomicroscope,the maximum possible size of the illuminating light beam from the slitlamp light source as the beam reaches an indirect ophthalmoscopy lens orthe eye of the patient is no more than 12 mm in diameter. If an indirectophthalmoscopy lens is utilized for examination, only a part of theindirect ophthalmoscopy lens is illuminated by the incident light beamfrom the slit lamp light source, and correspondingly, only a similarlysized image of the indirect ophthalmoscopy lens on the fundus of the eyewill be formed and only a portion of the fundus will be illuminateddirectly, although some indirect illumination may be generated fromlight scattering within the eye. The brightly illuminated portion of theaerial image of the fundus produced by an indirect ophthalmoscopy lensthus will be limited in size and significantly smaller then it would behad the indirect ophthalmoscopy lens been fully illuminated by theincident light beam from the biomicroscope. By utilizing a lens havingrefractive power in the optical device of the invention, the incidentlight beam may be increased in size such that the entire extent of anindirect ophthalmoscopy lens will be illuminated. Full illumination ofthe indirect ophthalmoscopy lens will result in formation of an image ofthe light source at a point near the center of the pupil of the eye,from which light will diverge to form a broad illuminated area of thefundus the size of the image of the indirect ophthalmoscopy lens on thefundus. Light is diffusely reflected from all illuminated points in thefundus and from each illuminated point a diverging bundle of light rayspass through the pupil of the eye and through the cornea to be incidentupon the indirect ophthalmoscopy lens. The indirect ophthalmoscopy lenswill then form a real inverted aerial image of the fundus which isviewed through the biomicroscope, and which will have the same level ofillumination across its entire extent and will appear, when viewedthrough the biomicroscope, to fill the entire indirect ophthalmoscopylens. It should be evident that a lens having refractive power mayinclude a filtering capacity if constructed as a composite lens or maybe used in conjunction with a separate filter lens. The characteristicsof the optical device having a lens with refractive power will bedescribed in more detail as the description proceeds.

It should be evident from the foregoing that the optical device 28 canbe instantly positioned with its lens portion in front of and coaxialwith the projecting or condensing lens of the slit lamp biomicroscopeand just as simply be displaced from this position. The device makes itvery practical for the slit lamp biomicroscope to be used in its usualfashion in examining the eye, and while the patient is still seated infront of the slit lamp, to position the optical device 28 in front ofthe condensing lens to modify the optical characteristics of theilluminating light so as to perform various other examination techniquesas desired. In the preferred embodiment, the optical device 28 ispositioned directly adjacent the condensing or projecting lens 20 of theslit lamp light source, although it may be positioned at some otherconvenient distance from the condensing lens, between the condensinglens and the oblique mirror 22 of the biomicroscope. As seen in FIG. 5,the height of the body portion 32 as indicated at B is such that thebody portion may be slid up against other supporting structure of theillumination system so as to automatically position the lens holdingportion 44 at the proper location to be rotated into a closely adjacentposition relative to condensing lens 20. It should also be evident thatanother optical device 28 may be used in conjunction with anothersupporting rod 34 on the opposite side of condensing lens 20, which maysimilarly be rotated into an out of position in the path of theilluminating light. In such a situation, it may be desirable to providea spacer in conjunction with the body portion 32 which can be slid ontothe supporting bar 34! at its narrowed portion 36 in a similar manner toeasily adjust the position of the lens holding portion 44 relative tothe condensing lens 20. Such a spacer may simply comprise asemi-circular body portion having a predetermined height and a gap so asto be slid over the narrowed portion 36 of the support bar 34 to be usedin conjunction with the optical device 28.

Turning now to FIG. 6, an alternate embodiment of the optical device isshown to include a plurality of lenses which may be selectivelypositioned in the path of the illuminating light as desired by the user.In this embodiment, the optical device 60 again may include asemi-circular body portion 62 having a gap 64 therein which is adaptedto slip over a narrowed portion of supporting bars on the illuminationsystem of the biomicroscope in a similar manner to that previouslydescribed. The optical device 60 may further comprise a plurality oflens holding portions 66, 68, etc., which are secured to the bodyportion 62 by means of a pin or the like at 70. The lens holdingportions 66 and 68 may therefore rotate or pivot about pin 70 so as toselectively position each of the plurality of lens holding portions intothe path of the illuminating light beam separately or in conjunctionwith one another. Each of the lens holding portions 66,68, etc. willinclude a lens portion 72,74, etc. which may be of the types of lensespreviously described to provide the desired modification of the opticalcharacteristics of the illuminating light beam.

Another type of slit lamp biomicroscope is shown in FIG. 7, which issimilar to those manufactured by Zeiss or the Bausch & Lomb Thorpe slitlamp. This type of slit lamp includes many of the same features asdescribed with respect to the biomicroscope of FIG. 1, but does notinclude the same illumination system as described therein. In thebiomicroscope 80, the illumination system 82 comprises a condensing lens84 forming an exit opening for light rays to emerge from theillumination system 82. The condensing lens 84 is positioned relative toan oblique mirror 86 in association with housing 81. With such a design,the optical device 88 is operatively positioned to allow modification ofthe illuminating light beam similarly to that previously described. Asseen more clearly in FIG. 8, a first embodiment of the optical device 88includes a lens holding portion 90 which is adapted to be placed intothe path of the illuminating light beam passing through the condensinglens 84. The lens holding portion 90 has a lens 92 secured to therein ina manner similar to that previously described to allow easy removal andreplacement of the lens 92 by the user for adaptability of the device tovarious examination procedures. The lens holding portion 90 is pivotallysecured to a first body portion 94 which is adapted to be secured to thehousing 81 of the condensing lens 84 and oblique mirror 86 of thebiomicroscope 80. The first body portion 94 may be secured by means ofan adhesive tab 96 or other suitable means to secure it in its operativeposition on the biomicroscope. A hinge means 98 attaches the first bodyportion 94 to the lens holding portion 90 such that lens holding portion90 can pivot about the axis of hinge 98.

In operation, the first body portion 94 is placed on the triangularlyshaped housing 81 such that the hinge 98 is positioned at the pinnacleof the housing as seen in FIG. 7. The lens holding portion 90 may thenbe pivotaly swung into and out of its operative position adjacent and infront of the condensing lens 84 as seen in FIG. 7. To facilitate suchmovement, a finger tab portion 100 may be provided on lens holdingportion 90.

An alternative embodiment of the optical device for use with thebiomicroscope as seen in FIG. 7 is shown in FIG. 9 at 110, which againincludes a lens holding portion 112 including a lens 114 and finger tabportion 116 similar to that described with reference to FIG. 8. The lensholding portion varies in that it is removably attached to a first bodyportion 118 to allow replacement of the lens holding portion to providea variety of lenses for use with the device. The means by which lensholding portion 112 may be attached to first body portion 118 maycomprise a post 120 having an enlarged head 122 at the distal endthereof, wherein post 120 may be snap fit into a suitable slot formed infirst body portion 118. The post 120 will be rotatable in the slot toallow the pivoting motion of lens holding portion 112 relative to thefirst body portion 118, so as to pivot the lens 114 into and out of thepath of the illuminating light beam in the region adjacent thecondensing lens 84. The first body portion may include downwardlyextending wing portions 124 which are adapted to slip over thetriangularly shaped housing 81. The housing 81 of the biomicroscope willnormally have narrowed portions at the location adjacent the microscopehead of the biomicroscope to facilitate clear binocular vision withoutinterference from the housing. The first body portion 118 may beconstructed of a resilient plastic type material to allow a slightspreading apart of the wing portions 124 for engagement to the housing81 of the biomicroscope. The wing portions 124 may be easily slippedonto the housing 81 at the location of the narrowed portions, and thenslid upwardly so as to be frictionally engaged on the housing in theoperative position to allow pivoting of lens holding portion 112 intoand out of the illuminating light path. It should be evident that theembodiment of FIG. 9 allows the user to select any desired lens type foruse with the body portion 118 which may then be simply positioned on thelens housing of the biomicroscope for operation.

Turning now to FIG. 10, there is shown a schematic illustration of theoptics of a slit lamp biomicroscope wherein the optical device of theinvention is utilized as a beam enlarger to increase the divergence ofthe illuminating light beam from the slit lamp light source which willbe incident upon an indirect ophthalmoscopy lens as an example. Asmentioned previously, when the biomicroscope is used for indirectophthalmoscopy, the indirect ophthalmoscopy lens will normally have arelatively large diameter lens such as described in U.S. Pat. No.4,738,521. In state-of-the-art slit lamp biomicroscopes, the maximumsize of the illuminating light beam as the beam reaches the indirectophthalmoscopy lens positioned adjacent the eye under examination, is nomore than 12 mm in diameter. Thus, the maximum possible size of theilluminating light beam is less than the diameter of the indirectophthalmoscopy lens, and it therefore may be desirable to increase thesize of the incident light beam upon the indirect ophthalmoscopy lens tothe extent that the entire indirect ophthalmoscopy lens is illuminated.By illuminating the indirect ophthalmoscopy lens to its full extent, theaerial image of the fundus will be uniformly illuminated and willcorrespond to the full extent of the indirect ophthalmoscopy lens.

Additionally, in an emmettopic eye, the aerial image of the fundusproduced by an indirect ophthalmoscopy lens as seen of a slit lampbiomicroscope, will be in the anterior focal plane of the indirectophthalmoscopy lens. With an adequately dilated pupil and the slitaperture fully opened, the produced aerial image will be approximatelyone centimeter in diameter and will be coplanar with the effective lightsource and object plane of the biomicroscope. Alternatively, in a myopiceye, the aerial image will be slightly closer to the indirectophthalmoscopy lens, and conversely with hypermetropia, the image willbe slightly farther from the indirect ophthalmoscopy lens. In thesesituations, the biomicroscope must be moved slightly closer or slightlyfurther away from the indirect ophthalmoscopy lens respectively, inorder to allow sharp focusing upon the aerial image produced by thelens. Should the pupil of the examined eye be of relatively smalldiameter, light from an indirect ophthalmoscopy lens will be blockedfrom the fundus, which will result in a decrease of brightness and sizeof the corresponding aerial image produced by the lens. Therefore, itmay be desirable to reduce the size of the converged incident light beamfrom a slit lamp biomicroscope at the center of the entrance pupil ofthe examined eye so as to permit illumination of the funduscorresponding to the full extent of the pupillary aperture. By reducingthe size of the pupillary image of the light source filament at thecenter of the pupil of the examined eye, indirect ophthalmoscopyperformed with the slit lamp biomicroscope on eyes with undilated pupilsmay be facilitated.

Turning to FIG. 10, an example of the use of the optical device toaccomplish the above goals is shown in relation to the opticalcharacteristics of the slit lamp biomicroscope in use for indirectophthalmoscopy. The slit lamp biomicroscope includes a light source 150being a small filament within the biomicroscope and producing divergingbundles of light rays 152 which are directed toward lenses 154. Thelenses 154 produce a converging bundle of light rays directed towardaperture stop 156 of the biomicroscope. The condensing lens 158 of thebiomicroscope will thus receive converging bundles of light rays fromthe aperture stop 156, and will produce diverging bundles of light rayswhich are directed toward the examined eye 164. The optical device 160of the invention is positioned closely adjacent the condensing lens 158of the biomicroscope as previously described, and in this embodiment isshown as a negative power lens. It is well known that a negative lensadds divergence to a homocentric beam of light incident upon the lens,and thus the divergence of the homocentric bundles of light rays fromcondensing lens 158 is increased so that the light rays incident upon anindirect ophthalmoscopy lens 162 will fully illuminate the lens 162 asdesired. It can be seen in this schematic illustration that the use ofthe optical device 160 having a negative power lens will result in arepositioning of the effective and virtual light source to a position166 which is closer to the condensing lens 158. A wider beam of light isthus produced by the lens of the optical device 160 even though the sizeof the aperture stop 156 remains unchanged. The diameter of the aperturestop 156 may be the maximum diameter, wherein the power of the lens inthe optical device 160 is chosen to increase divergence from condensinglens 158 to achieve maximum illumination of the indirect ophthalmoscopylens 162. Alternatively, the aperture stop 156 may be less then maximum,wherein an increase in power of the lens in the optical device 160 canresult in a compensatory widening of the beam of light refracted throughthe lens of the optical device 160. The adaptability of the opticaldevice to allow the use of various lenses therein may thus allow theslit aperture to be varies while optimizing the widening of the beam.

As an alternative embodiment, the lens of the optical device 160 may bea positive power lens, wherein it is well known that a positive lenswill add convergence to an incident homocentric beam of light incidentupon the positive lens. The use of a positive power lens may thus resultin a repositioning of the effective and real light source of the slitlamp biomicroscope to a position closer to a condensing lens 158, whileproducing a wider beam of light with the diameter of aperture stop 156remaining unchanged. Similar to that described with reference to thenegative power lens 160 of FIG. 10. It should be recognized that theschematic illustration of the optical path from the slit lamp lightsource to an examined eye is merely an example, and the slit lampbiomicroscope illuminating system may include an oblique mirror toredirect the light beam to the indirect ophthalmoscopy lens or examinedeye. In either case, the optical device 160 being of negative orpositive refractive power is positioned closely adjacent to thecondensing lens 158 of the biomicroscope to achieve the desired beamenlargement for full illumination in the indirect ophthalmoscopy lens162 as shown in FIG. 10. In this way, the maximum area of the fundus 168of the eye is illuminated which will produce the maximum size aerialimage from the indirect ophthalmoscopy lens 162.

It should be understood that the power of the lens utilized in theoptical device of the invention to produce adequate divergence of theincident light beam may vary with the distance of the lens from thecondensing lens of the slit lamp, wherein an increased distance from thecondensing lens will require a stronger refractive powered lens. As anexample where the optical device of the invention is positioned closelyadjacent to the condensing lens of the biomicroscope, lens powersranging from -20 diopters to +20 diopters may be adequate for thepresent state-of-the-art slit lamp biomicroscopes available fromdifferent manufacturers, and for the amounts of divergence of theincident light beam needed for the range of diameters of indirectophthalmoscopy lenses normally used in conjunction with examinationsusing slit lamp biomicroscopes. The lenses having refractive power maybe used in conjunction with filtering lenses if desired, by means ofproviding a plurality of lenses on the optical device or be utilizationof a plurality of devices with the slit lamp biomicroscope.

The use of a lens which has refractive power will also provide thedesired enhancement of the image produced by an indirect ophthalmoscopylens when used to examine eyes with small pupillary apertures. As anexample, when the slit of the slit lamp is fully opened, the effectivelight source is the circular image of the aperture of the slit lampwhich is generally about one centimeter in diameter. The incident lightbeam on an indirect ophthalmoscopy lens will be only slightly largerthan the sharply focused circular image of the aperture since theindirect ophthalmoscopy lens is held at a distance from the object planeof the biomicroscope which is equal to the short anterior focal distanceof the indirect ophthalmoscopy lens, which itself is held approximatelythe same distance from the entrance pupil of the eye. The convergingbundles of parallel light rays from the effective slit lamp light sourcegenerated at the slit lamp aperture are directed toward a relativelylarge circular cross-sectional area in the secondary focal plane of theindirect ophthalmoscopy lens. The bundles of parallel light rays arethen refracted by the cornea and aqueous humor of the examined eye, andthe cross-sectional area is formed at approximately the pupil of theexamined eye. The light rays will be further refracted by thecrystalline lens and vitreous humor of the eye to a focus at the fundusof the examined eye. As an example, using a large diameter indirectophthalmoscopy lens, the circular cross-sectional area at the pupil willbe approximately 4 mm in diameter with a 60 diopter lens. If the pupilof the examined eye is smaller than the 4 mm diameter, some of the lightfrom the indirect ophthalmoscopy lens will be blocked from the fundus bythe pupillary aperture. Such blockage of the illuminating light willresult in a decrease of brightness and a decrease in size of theilluminated area of the fundus with a corresponding effect upon theaerial image produced by the indirect ophthalmoscopy lens. The size ofthe converged incident light beam from the slit lamp light source may bereduced by the optical device of the invention at the center of theentrance pupil of the examined eye so as to permit illumination of thefundus corresponding to the full extent of the fully illuminatedindirect ophthalmoscopy lens through a small pupil.

The interrelated objects of producing an enlargement of the incidentlight beam on an indirect ophthalmoscopy lens or a reduction of size ofthe image of the slit lamp light source at the pupil of the examined eyeare accomplished by the dissociation and repositioning of the effectiveslit lamp light source from its coplanar position with respect to theobject plane of the biomicroscope by means of the optical device of theinvention. These aspects along with the desirable aspects of providingmodification of the optical characteristics of the light source be meansof filters or the like provide an optical device which allows greatadaptability of the slit lamp biomicroscope.

It will be evident to those skilled in the art that the invention is notlimited to the details of the foregoing illustrative embodiments, andthat the present invention may be embodied in other specific formswithout departing from the spirit or scope thereof. Therefore, thepresent embodiments are to be considered as illustrative only and notrestrictive as to the scope of the invention as defined in the appendedclaims.

I claim:
 1. A lens attachment for a slit lamp biomicroscope comprising;a microscope means and an illumination system having a housing associated therewith, wherein said illumination system housing includes an exit opening through which illuminating light is directed toward the eye of a patient to be examined with said lens attachment comprising a mounting means which is selectively positioned and supported relative to said exit opening of said illumination system housing at a predetermined position; at least one lens associated with said mounting means to allow said at least one lens to be selectively disposed in a position between said exit opening of said illumination system and the eye of a patient in the path of the illuminating light beam generated by said illumination system without interfering with the optical pathway of said microscope means to allow selective modification of the optical characteristics of the illuminating light beam.
 2. The optical device of claim 1, wherein, said at least one lens is of negative refractive power, with a dioptric value within the range of -1.0 to -20.0 diopters.
 3. The optical device of claim 1, wherein, said at least one lens is of positive refractive power, with a dioptric value within the range of 1.0 to 20.0 diopters.
 4. The optical device of claim 1, wherein, said at least one lens is made of homogenous transparent plastic.
 5. The optical device of claim 1, wherein, said at least one lens is made of homogenous transparent glass.
 6. The optical device of claim 1, wherein, said at least one lens is a filter which will filter out a predetermined portion of the spectrum of light passing therethrough.
 7. The optical device of claim 6, wherein, said filter is a color filter which will filter out a portion of the visible spectrum of the light passing therethrough.
 8. The optical device of claim 6, wherein, said filter is a polarizing filter acting to polarize the light passing therethrough in a specific direction.
 9. The optical device of claim 1, wherein, said lens is a compound lens which comprises at least two lenses which act together to modify said illuminating light beam.
 10. The optical device of claim 1, wherein, said mounting means includes means to selectively secure at least one lens therein so as to enable selective removal and replacement of said at least one lens.
 11. The optical device of claim 1, wherein, said mounting means includes at least one lens holding portion which is selectively detachable from said mounting means to enable selective replacement of said at least one lens holding portion and thereby of said at least one lens.
 12. The optical device of claim 1, wherein, said mounting means includes a plurality of lens holding portions, each of which include at least one lens with each being selectively positionable within the path of the illuminating light beam.
 13. The optical device of claim 1, wherein, said mounting means has a semi-circular portion with a longitudinal gap therein which is dimensioned to be selectively positionable on the support structure of said illumination system of the slit lamp biomicroscope.
 14. The optical device of claim 13, wherein, said semi-circular portion is dimensioned so as to have a slightly smaller diameter than the diameter of said support structure so as to enable frictional engagement of said mounting means to said support structure and to allow selective rotation thereof on said support structure.
 15. The optical device of claim 1, wherein, said mounting means includes at least one lens holding portion which is hingedly engaged to said mounting means to allow said at least one lens holding portion to pivot into and out of the path of the illuminating light.
 16. The optical device of claim 1, wherein, said mounting means includes means to adhere it to said slit lamp biomicroscope in a predetermined position and includes at least one lens holding portion wherein said at least one lens holding portion is selectively positionable in the path of the illuminating light. 